\b reports false-positives in Indic strings involving combining marks

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = None
created_at = <Date 2017-12-02.13:28:09.501>
labels = ['expert-regex', 'type-bug', '3.7']
title = '\\b reports false-positives in Indic strings involving combining marks'
updated_at = <Date 2017-12-02.18:28:37.269>
user = 'https://bugs.python.org/jamadagni'

bugs.python.org fields:

activity = <Date 2017-12-02.18:28:37.269>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = False
closed_date = None
closer = None
components = ['Regular Expressions']
creation = <Date 2017-12-02.13:28:09.501>
creator = 'jamadagni'
dependencies = []
files = []
hgrepos = []
issue_num = 32198
keywords = []
message_count = 2.0
messages = ['307430', '307446']
nosy_count = 4.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'serhiy.storchaka', 'jamadagni']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32198'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7']